Coaxial contacts for 3d logic and memory

ABSTRACT

A semiconductor device includes a coaxial contact that has conductive layers extending from local interconnects and being coupled to metal layers. The local interconnects are stacked over a substrate and extend laterally along a top surface of the substrate. The metal layers are stacked over the local interconnects and extend laterally along the top surface of the substrate. The conductive layers are close-shaped and concentrically arranged, where each of the local interconnects is coupled to a corresponding conductive layer, and each of the conductive layers is coupled to a corresponding metal layer. The semiconductor device also includes insulating layers that are close-shaped, concentrically arranged, and positioned alternately with respect to the conductive layers so that the conductive layers are spaced apart from one another by the insulating layers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/851,990 filed on May 23, 2019, the entire contents of which isincorporated herein by reference.

FIELD OF THE INVENTION

This disclosure relates to methods of microfabrication, includingfabrication of semiconductor devices.

BACKGROUND

In the manufacture of a semiconductor device (especially on themicroscopic scale), various fabrication processes are executed such asfilm-forming depositions, etch mask creation, patterning, materialetching and removal, and doping treatments. These processes areperformed repeatedly to form desired semiconductor device elements on asubstrate. Historically, with microfabrication, transistors have beencreated in one plane, with wiring/metallization formed above the activedevice plane, and have thus been characterized as two-dimensional (2D)circuits or 2D fabrication. Scaling efforts have greatly increased thenumber of transistors per unit area in 2D circuits, yet scaling effortsare running into greater challenges as scaling enters single digitnanometer semiconductor device fabrication nodes. Semiconductor devicefabricators have expressed a desire for three-dimensional (3D)semiconductor circuits in which transistors are stacked on top of eachother.

SUMMARY

3D integration has been seen as the most viable option to continuesemiconductor scaling in spite of inevitable saturation in criticaldimension scaling. As a contacted gate pitch reaches its scaling limitdue to manufacturing variability and electrostatic device limitations,two-dimensional transistor density scaling stops. Even experimental newtransistor designs, such as vertical channel gate-all-aroundtransistors, that may be able to one day overcome these contacted gatepitch scaling limits, do not promise to get semiconductor scaling backon track because resistance, capacitance, and reliability concernsprevent wire pitch scaling, thereby limiting the density with whichtransistors can be wired into circuits.

3D integration, i.e., the vertical stacking of multiple devices, aims toovercome these scaling limitations by increasing transistor density involume rather than area. This idea has been successfully demonstratedand implemented by the flash memory industry with the adoption of 3DNAND. 3D integration of logic devices, however, has considerablechallenges. One challenge to achieve scaling density in 3D integrateddevices is a minimum pitch with which subsequent device levels can becontacted from the wiring levels above.

Techniques herein provide a coaxial contact (or coaxial contactstructure) that selectively connects individual levels (e.g.,source-side/drain-side local interconnects, gate electrodes) in adevice-stack (also referred to transistor stack) to corresponding levels(e.g., metal layers, metal levels, M0 level, M1 level) in a wiring-stackwithout a need to stagger either level in a stair-cased formation. Inaddition to the structure of the coaxial contact, a manufacturing flowto build such a structure and a cell-architecture is also disclosed.

Of course, an order of the manufacturing steps disclosed herein ispresented for clarity sake. In general, these manufacturing steps can beperformed in any suitable order. Additionally, although each of thedifferent features, techniques, configurations, etc. herein may bediscussed in different places of the present disclosure, it should benoted that each of the concepts can be executed independently from eachother or in combination with each other. Accordingly, the presentdisclosure can be embodied and viewed in many different ways.

It should be noted that this summary section does not specify everyembodiment and/or incrementally novel aspect of the present disclosureor claimed invention. Instead, this summary only provides a preliminarydiscussion of different embodiments and corresponding points of noveltyover conventional techniques. For additional details and/or possibleperspectives of the invention and embodiments, the reader is directed tothe Detailed Description section and corresponding figures of thepresent disclosure as further discussed below.

According to an aspect of the disclosure, a semiconductor device isprovided. The semiconductor device is formed over a substrate, andincludes conductive layers. The conductive layers extend from localinterconnects and are coupled to metal layers that are stacked over thelocal interconnects. The local interconnects are stacked over thesubstrate and extend laterally along a top surface of the substrate.Moreover, the metal layers extend laterally along the top surface of thesubstrate. The conductive layers are close-shaped, concentricallyarranged, and extend in a pillar shape, where each of the localinterconnects is coupled to a corresponding conductive layer from theconductive layers, and each of the conductive layers is coupled to acorresponding metal layer from the metal layers. Further, thesemiconductor device includes insulating layers. The insulating layersare close-shaped, concentrically arranged, and positioned alternatelywith respect to the conductive layers so that the conductive layers arespaced apart from one another by the insulating layers.

The conductive layers can have bottom ends, where the bottom ends arestaggered and coupled to one or more of the local interconnects so thateach of the local interconnects is coupled to a respective conductivelayer from the conductive layers. The conductive layers can also havetop ends, where the top ends are staggered and coupled to one or more ofthe metal layers so that each of the conductive layers is coupled to arespective metal layer from the metal layers.

In some embodiments, the conductive layers can have at least one of atube configuration, or a cylinder configuration. The tube configurationor the cylinder configuration can have a tapered profile.

The semiconductor device can further have transistor pairs that arestacked over the substrate, where each of the transistor pairs includesa n-type transistor and a p-type transistor that are stacked over oneanother. The n-type transistor can have a source region and a drainregion that are positioned at two ends of a n-type channel region of then-type transistor. Each of the source region and drain region of then-type transistor is coupled to a respective local interconnect. Then-type channel region is surrounded by a n-type gate structure. Thep-type transistor can have a source region and a drain region that arepositioned at two ends of a p-type channel region of the p-typetransistor. Each of the source region and drain region of the p-typetransistor is coupled to a respective local interconnect, and the p-typechannel region is surrounded by a p-type gate structure.

The semiconductor device can also have gate electrodes that are stackedover the substrate. The gate electrodes can be electrically coupled togate structures of the transistor pairs. At least one of the conductivelayers extends from one of the gate electrodes, and is coupled to theone of the gate electrodes.

The insulating layers can have bottom ends and top ends. The bottom endsare staggered so that a bottom end of each of the insulating layers islevel with a bottom end of a corresponding conductive layer from theconductive layers. The insulating layers can also have top ends. The topends are staggered so that a top end of each of the insulating layers islevel with a top end of a corresponding conductive layer from theconductive layers.

According to another aspect of the disclosure, a method for forming asemiconductor device is provided. In the disclosed method, a firstopening is formed in a dielectric stack that is positioned over asubstrate. The first opening can have a cylinder shape with a firstsidewall and a first bottom. A first conductive layer is subsequentlydeposited along the first sidewall of the first opening and a firstinsulating layer is deposited along an inner sidewall of the firstconductive layer. The first conductive layer and the first insulatinglayer can be close-shaped and are concentrically arranged. A bottom ofthe first conductive layer and a bottom of the first dielectric layerare positioned on the first bottom of the first opening.

The dielectric stack is then etched along an inner sidewall of the firstinsulating layer so as to form a second opening. The second openingextends into the dielectric stack and has a second sidewall and a secondbottom. The second sidewall is formed along the inner sidewall of thefirst dielectric layer and further extending into the dielectric stack.The second bottom of the second opening is positioned below the bottomsof the first conductive layer and first insulating layer. A secondconductive layer is further formed along the second sidewall of thesecond opening and a second insulating layer is formed along an innersidewall of the second conductive layer. A bottom of the secondconductive layer and a bottom of the second insulating layer arepositioned on the second bottom of the second opening so that the bottomof the second conductive layer is positioned below the bottom of thefirst conductive layer to form a staggered configuration.

In some embodiments, the disclosed method can further includealternately etching the dielectric stack and depositing a conductivelayer and an insulating layer sequentially so that conductive layers andinsulating layers are formed in the dielectric stack to meet apredefined number of conductive layers and a predefined depth. Theconductive layers and the insulating layers are positioned alternatelywith a closed-shape and concentrically arranged. The first conductivelayer is an outermost layer of the conductive layers. The conductivelayers have bottom ends, where the bottom ends are staggered and coupledto one or more of local interconnects so that each of the localinterconnect is coupled to a respective conductive layer. The localinterconnects are stacked over the substrate and extend laterally alonga top surface of the substrate.

The method can further include depositing a dielectric capping layerover the insulating layers, the conductive layers and the dielectricstack, where the insulating layers, the conductive layers and thedielectric stack are coplanar. The method then includes performing afirst vertical etch into the dielectric stack to form a vertical trenchopening around an outer sidewall of the first conductive layer, wherethe vertical trench opening extends into the dielectric stack with afirst depth and uncover a first portion of the first conductive layer.

A first lateral etch is then performed to remove the uncovered firstportion of the first conductive layer and a first portion of the firstinsulating layer that is adjacent to the uncovered first portion of thefirst conductive layer, where the first lateral etch further uncovers afirst portion of the second conductive layer. A second vertical etch isthen performed into the dielectric stack to extend the vertical trenchopening into the dielectric stack with a second depth and uncover asecond portion of the first conductive layer. The method subsequentlyincludes performing a second lateral etch, where the second lateral etchremoves (i) the uncovered second portion of the first conductive layerand a second portion of the first insulating layer that is adjacent tothe uncovered second portion of the first conductive layer, so as touncover a second portion of the second conductive layer; and (ii) theuncovered first portion of the second conductive layer and a firstportion of the second insulating layer that is adjacent to the uncoveredfirst portion of the second conductive layer, so as to uncover a firstportion of a third conductive layer of the conductive layers, where thethird conductive layer is formed along an inner sidewall of the secondinsulating layer.

The method can further include alternately performing a vertical etchand a lateral etch so that each of the conductive layers is uncovered inthe vertical trench opening, and top ends of the conductive layers arestaggered and coupled to one or more of metal layers. Accordingly, eachof the conductive layers is coupled to a respective metal layer, wherethe metal layers are stacked over the local interconnects.

According to yet another aspect of the disclosure, a semiconductordevice is provided. The semiconductor device includes transistor pairsthat are stacked over a substrate. Each of the transistor pairs caninclude a n-type transistor and a p-type transistor that are stackedover one another. The semiconductor device also includes localinterconnects that are stacked over the substrate and extend along a topsurface of the substrate. The local interconnects are electricallycoupled to source regions and drain regions of the transistor pairs.

The semiconductor device further includes metal layers stacked over thelocal interconnects, and conductive layers. The conductive layers extendfrom the local interconnects and coupled to the metal layers. Theconductive layers are cl ose-shaped and concentrically arranged. Each ofthe local interconnects is coupled to a corresponding conductive layerfrom the conductive layers, and each of the conductive layers is coupledto a corresponding metal layer from the metal layers. The semiconductordevice can have insulating layers that are close-shaped, concentricallyarranged, and positioned alternately with respect to the conductivelayers so that the conductive layers are spaced apart from one anotherby the insulation layers.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1A is a schematic diagram of a related semiconductor device that isformed based on a 3D integrated CFET stack with stair-cased localinterconnects, in accordance with some embodiments.

FIG. 1B is a schematic view of a related semiconductor device that isformed based on a 3D integrated CFET stack with stair-cased localinterconnects, in accordance with some embodiments.

FIG. 2 is a schematic view of an exemplary coaxial contact, inaccordance with some embodiments.

FIGS. 3A-3H are schematic views of first exemplary intermediate steps ofmanufacturing an exemplary coaxial contact, in accordance with someembodiments.

FIGS. 4A-4I are schematic views of second exemplary intermediate stepsof manufacturing an exemplary coaxial contact, in accordance with someembodiments.

FIG. 5A is a schematic circuit diagram of an And-Or-Invert 22 (AOI22)cell, in accordance with some embodiments.

FIG. 5B is a top down layout view of an AOI22 cell implemented based ona CFET stack and coaxial contacts, in accordance with some embodiments.

FIG. 6A is a first cross-sectional layout view of an AOI22 cellimplemented based on a CFET stack and coaxial contacts, in accordancewith some embodiments.

FIG. 6B is a second cross-sectional layout view of an AOI22 cellimplemented based on a CFET stack and coaxial contacts, in accordancewith some embodiments.

FIG. 6C is a third cross-sectional layout view of an AOI22 cellimplemented based on a CFET stack and coaxial contacts, in accordancewith some embodiments.

FIG. 6D is a fourth cross-sectional layout view of an AOI22 cellimplemented based on a CFET stack and coaxial contacts, in accordancewith some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. In addition, the presentdisclosure may repeat reference numerals and/or letters in the variousexamples. This repetition is for the purpose of simplicity and clarityand does not in itself dictate a relationship between the variousembodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of theapparatus in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, material, orcharacteristic described in connection with the embodiment is includedin at least one embodiment, but do not denote that they are present inevery embodiment. Thus, the appearances of the phrases “in oneembodiment” in various places through the specification are notnecessarily referring to the same embodiment. Furthermore, theparticular features, structures, materials, or characteristics may becombined in any suitable manner in one or more embodiments.

Some conventional semiconductor structures, such as those formed in themicrofabrication of 3D NAND, for example, use stair-cased geometry.Stair-cased or step-shaped levels (e.g., word lines, localinterconnects) connect to corresponding stair-cased/step-shaped wiringlevels (e.g., metal 0 level, metal 1 level) to route stacked devicelayers to corresponding input and output signals. An adaptation of thisstair-casing approach for 3D logic is shown in FIGS. 1A and 1B. FIG. 1Ais a simplified cross-section of a substrate segment having a stack offour device layers and showing lateral local interconnects. Verticalcontacts land on local interconnects to connect devices to access-pinpositioned above a device stack. As shown in FIG. 1A, a 3D integratedcomplementary field effect transistor (CFET) stack 100 (also referred toas transistor stack 100, CFET stack 100, or CFET transistor stack 100)with stair-cased local interconnects is provided. The transistor stack100 can include four CFET devices 102-108 that are stacked over asubstrate (not shown). Each of the CFET devices can include a n-typetransistor and p-type transistor that are coupled to a respective input(e.g., inputs A-D). For example, the CFET 102 can include the n-typetransistor N3 and a p-type transistor P3. The transistor stack 100 canhave a plurality of local interconnects 112-126 that have a staircaseconfiguration. Each of the local interconnects is coupled to arespective transistor. The transistor stack 100 can further include aset of array of vertical contacts 110 that are coupled to and extendfrom the local interconnects 112-126. The set of array of verticalcontacts 110 can have top surfaces in-plane with each other, whilelength of each vertical contact or column is different depending on aheight and location of a landing step.

A poly gate runs through the stack left to right, with an active channelregion in the middle. P and N local interconnects and vertical contactsare shown in FIG. 1B. FIG. 1B is an illustration of contacts landing oneach of the local interconnects to contact subsequent source/drainregions from a given wiring level above. In other words, FIG. 1B showsan array of contacts landing on the stair-cased device stack. Anachievable minimum size of an overall stacked device arrangement isultimately limited by a required minimum landing area on each devicelevel.

As shown in FIG. 1B, a semiconductor device can be formed based on a 3Dintegrated CFET stack 200 (also referred to as transistor stack 200,CFET stack 200, or CFET transistor stack 200) with stair-cased localinterconnects. The CFET transistor stack 200 can include four CFETdevices 202-208 that are stacked over a substrate (not shown). Each ofthe four CFET devices can include a transistor pair that is formed by an-type transistor and a p-type transistor. For example, the CFET device202 can include a transistor pair that is formed by the n-typetransistor N3 and the p-type transistor P3. The n-type transistor can bepositioned over the p-type transistor. In some embodiments, the n-typetransistor and the p-type transistor can have a shared gate structure.The gate structure can surround a n-type channel region of the n-typetransistor and a p-type channel region of the p-type transistor. Thechannel region can have a sheet, wire or bar configuration. The n-typetransistor can have a source region and a drain region that arepositioned at two ends of the n-type channel region respectively, wherethe gate structure surrounds the n-type channel region, and positionedbetween the source region and the drain region of the n-type transistor.The p-type transistor can have a source region and a drain region thatare positioned at two ends of the p-type channel region respectively,where the gate structure surrounds the p-type channel region, andpositioned between the source region and the drain region of the p-typetransistor. Moreover, the gate structure can be electrically coupled toa gate electrode. The source region and the drain region can have asource local interconnect and a drain local interconnect respectively.

For example, the n-type transistor N3 and the p-type transistor P3 canhave a shared gate structure 212. The n-type transistor N3 has a sourceregion 218 and a drain region 216 that are position at two ends of then-type channel region. The n-channel region is surrounded by the gatestructure 212, where the gate structure 212 is positioned between thesource region 218 and the drain region 216. The p-type transistor P3 hasa source region 222 and a drain region behind the gate structure 212.The source region 222 and the drain region are positioned at two ends ofthe p-type channel region. Similarly, the p-type channel region issurrounded by the gate structure 212, where the gate structure 212 ispositioned between the source region 222 and the drain region of thep-type transistor P3.

The gate structure 212 can have one or more gate electrodes 214. Thegate electrodes 214 can be positioned at two ends of the gate structure212. The source region 218 and the drain region 216 of the n-typetransistor N3 can have a source local interconnect 226 and a drain localinterconnect 224 respectively. Similarly, the source region 222 of thep-type transistor P3 can have a source local interconnect 220, and thedrain region of the p-type transistor P3 can have a drain localinterconnect positioned behind the gate structure 212. FIG. 1B alsoillustrates a plurality of local interconnects 228-232 that are coupledto n-type transistors N4, N2, N1 respectively.

It should be noted that the transistor stack 200 can further include aplurality of dielectric layers (not shown in FIG. 1B) that separate thetransistor pairs from one another. The dielectric layers can alsoseparate a n-type transistor and a p-type transistor from one another ina transistor pair. The dielectric layers can further separates the localinterconnects (e.g., 220, 224-232 in FIG. 1B) from one another.

In the transistor stack 200, the gate electrodes and the source/drain(S/D) local interconnects (also referred to as source-side/drain-sidelocal interconnects) can have a staircase configuration. Further, aplurality of vertical contacts 210 are coupled to and extend from theS/D local interconnects or the gate electrodes. Therefore, the staircaseconfiguration of the gate electrodes and the S/D local interconnectsprovides an easy access to each transistor in the transistor stack 200,and avoids a complicated interconnect connection.

Although FIGS. 1A and 1B provide configurations enabling an area-scalingand routing congestion improvement for logic standard cells as well asSRAM memory cells, an achievable minimum size of an overall stackeddevice arrangement is ultimately limited by a required minimum landingarea on each device level. The minimum landing area of the localinterconnects illustrated in FIGS. 1A and 1B driven primarily by twoprocess constraints: lithographic resolution limit and lithographicplacement limit. The lithographic resolution refers to a smallest pitchthat can be patterned. Specifically, the lithographic resolution is thesmallest pitch on which the contact array (e.g., 210 in FIG. 1B) canland, or each contact within the array can land. The smallest pitch istypically limited by resolution limits of a given photolithographicsystem (e.g., scanner or stepper) that is used to expose a pattern. Thelithographic placement limit refers to additional space or toleranceneeded to compensate for pattern placement errors. A misplaced patterncan cause shorting of contacts to local interconnect structuresbelonging to devices on adjacent device levels. In other words, despitecapability of printing a small pattern, the pattern itself can bemisaligned from a combination of tool and wafer factors.

To achieve higher levels of device integration, techniques hereinprovide a vertical coaxial interconnect structure that is able toselectively connect individual levels (e.g., local interconnects) in adevice-stack to corresponding levels (e.g., M0 level, M1 level) in awring-stack without the need to stagger either level in a stair-casedformation. An exemplary structure is illustrated in FIG. 2, and anexemplary process flow is illustrated in FIGS. 3A-3H and FIGS. 4A-4I.

FIG. 2 is a schematic view of an exemplary coaxial contact (alsoreferred to as coaxial contact structure, vertical coaxial contact,vertical coaxial contact structure, vertical coaxial interconnectstructure) 300, in accordance with some embodiments. As shown in FIG. 2,a cross-section of the coaxial (or coax) contact 300 is shown thatconnects four levels of metal (also referred to as metal layers) 316-322to four levels of local interconnect 324-330. The coaxial contact 300can include a plurality of concentric layers of conductor (or conductivelayers) 302-308 and insulator (or insulating layers) 310-314 formingtubes or cylinders in a 3D space. Both ends (i.e., bottom and top ends)of the coaxial contact are staggered to allow selective connection ofsequential layers as indicated in labels A to D. For example,stair-cases in both levels (e.g., the local interconnects and the metallayers) to be connected from a conventional stair case are replaced by aset of concentric layers of conductors and insulators integrated intowhat is referred to herein as a coax contact (or coaxial contact). Astaggered line-end configuration exposes sequential concentric “tubes”or cylinders of conductors in the coax contact to subsequent levels ofmetal or local-interconnect in stacks being connected. For a particularlevel, the outer tube (e.g., 302) of the coaxial contact structure 300connects to a current metal (e.g., 316) or local-interconnect level(e.g., 324) while the insulating layer (e.g., 310) protects the nextconductor tube (e.g., 304) from shorting to this particular level (e.g.,316 or 324).

Still referring to FIG. 2, the conductive layers 302-308 can extend fromthe local interconnects 324-330 and coupled to the metal layers (ormetal levels, or M0 levels) 316-322 that are stacked over the localinterconnects 324-330. The local interconnects 324-330 are stacked overa substrate (not shown) and extend laterally along a top surface of thesubstrate. The metal layers 316-322 can also extend laterally along thetop surface of the substrate. The conductive layers 302-308 can beclose-shaped, concentrically arranged, and extend in a pillar shape.Each of the local interconnects 324-330 is coupled to a correspondingconductive layer from the conductive layers 302-308, and each of theconductive layers 302-308 is coupled to a corresponding metal layer fromthe metal layers 316-322. For example, the conductive layer 304 extendsfrom the local interconnect 326 and coupled to the local interconnect326 and the metal layer 318.

In some embodiments, the conductive layers are close-shaped so thatcross-sections of the conductive layers 302-308 obtained along adirection parallel to the substrate can have a closed-loop configurationformed in a circular geometry. However, other geometries, such assquare, octagonal, rectangle, oval, triangle, or any other geometricshapes can also be applied according to circuit designs.

In some embodiments, the conductive layers are close-shaped so that theconductive layers 302-308 can extend in the pillar shape, and the pillarshape can have a tube configuration, or a cylinder configuration. Forexample, the conductive layer 308 can have a cylinder configuration andthe conductive layer 302 can have a tube configuration. In someembodiment, the tube configuration or the cylinder configuration can hasa tapered profile, which means that critical dimensions (CDs) of the topends of the conductive layers are larger than the CDs of the bottom endsof the conductive layers.

As shown in FIG. 2, the coaxial contact 300 can further include aplurality of insulating layers 310-314 that are close-shaped,concentrically arranged, and positioned alternately with respect to theconductive layers. Accordingly the conductive layers 302-308 are spacedapart from one another by the insulating layers 310-314. For example,the conductive layers 302 and 304 are separated by the insulating layer310, where the insulating layer 310 surrounds the conductive layer 302and the conductive layer 304 surrounds the insulating layer 310.

The conductive layers 302-308 can have bottom ends. The bottom ends arestaggered and coupled to one or more of the local interconnects 324-330so that each of the local interconnects 324-330 is coupled to arespective conductive layer from the conductive layers. For example, abottom end of the conductive layer 302 and a bottom end of theconductive layer 304 have a staggered configuration. The conductivelayer 302 is coupled to the local interconnect 324, and the conductivelayer 304 is coupled to the local interconnect 326 respectively. Theconductive layers 302-308 can have top ends. The top ends are staggeredand coupled to one or more of the metal layers 316-322 so that each ofconductive layers is coupled to a respective metal layer from the metallayers. For example, a top end of the conductive layer 302 and a top endof the conductive layer 304 have a staggered configuration. Theconductive layer 302 is coupled to the metal layer 316, and theconductive layer 304 is coupled to the metal layer 318 respectively.

In some embodiments, the conductive layers can land on top surfaces ofthe local interconnects so that each of the conductive layer can form asurface contact with a corresponding local interconnect. In someembodiments, the conductive layers can extend through the localinterconnects so that each of the conductive layers can form asurrounding contact with a corresponding local interconnect. Similarly,in an example, the conductive layers can be positioned beneath the metallayers so that each of the conductive layers can form a surface contactwith a corresponding metal layer. In another example, the conductivelayers can extend through the metal layers so that each of theconductive layers can form a surrounding contact with a correspondingmetal layer. In an exemplary embodiment of FIG. 2, the conductive layersextend through the local interconnects at the bottom ends and extendthrough the metal layers at the top ends.

Still referring to FIG. 2, the insulating layers 310-314 can have bottomends. The bottom ends are staggered so that a bottom end of each of theinsulating layers can be level with a bottom end of a correspondingconductive layer from the conductive layers. The insulating layers canalso have top ends. The top ends are staggered so that a top end of eachof the insulating layers can be level with a top end of a correspondingconductive layer from the conductive layers. For example, the bottom endof insulating layer 310 and the bottom end of conductive layer 302 arecoplanar, and the top end of insulating layer 310 and the top end ofconductive layer 302 are coplanar.

It should be noted that FIG. 2 is merely an example. The coaxial contact300 can include any number of conductive layers, and the conductivelayers can further be coupled to one or more gate electrodes or othercomponents. Further, the local interconnects and the metal layers can becoupled to a CFET transistor stack (not shown). The CFET transistorstack can have a similar configuration to the CFET stack 200. Forexample, similar to CFET stack 200 that is shown in FIG. 1B, the CFETtransistor stack can have a plurality of transistor pairs that arestacked over the substrate. Each of the transistor pairs includes an-type transistor and a p-type transistor that are stacked over oneanother. The n-type transistor has a source region and a drain regionthat are positioned at two ends of a n-type channel region of the n-typetransistor. Each of the source region and drain region of the n-typetransistor is coupled to a respective local interconnect. The n-typechannel region is surrounded by a n-type gate structure. The p-typetransistor can have a source region and a drain region that arepositioned at two ends of a p-type channel region of the p-typetransistor. Each of the source region and drain region of the p-typetransistor can be coupled to a respective local interconnect. The p-typechannel region is surrounded by a p-type gate structure. Further, aplurality of gate electrodes that are stacked over the substrate, andelectrically coupled to gate structures of the transistor pairs, whereat least one of the conductive layers extends from one of the gateelectrodes, and is coupled to the one of the gate electrodes. Comparingto the local interconnects (e.g., 226-232) in FIG. 1B, the localinterconnects (e.g., 324-330) and/or the metal layers (e.g., 316-322) inthe present disclosure do not need a stair-cased configuration after theimplementation of the coaxial contacts. Accordingly, the lithographicresolution limit and lithographic placement limit that are associatedwith the stair-cased configuration can be exceeded.

One process flow to build such a coaxial contact (or coaxial contactstructure) is illustrated in FIGS. 3A-3H and FIGS. 4A-4I. FIGS. 3A-3Hillustrate cross-sectional segments of formation of a coaxial contactstructure to show bottom line-end stagger. That is, staggered reveal ofeach coaxial contact of a coaxial contact structure. In FIG. 3A, a firstvertical etch is executed to define a first opening (form a hole) 404within a dielectric stack 402 so that successive layers of the coaxialcontact can be formed. The first opening 404 can have a first sidewall404 a and a first bottom 404 b. In FIG. 3B, the initial vertical etch isfollowed by sidewall deposition of a conductor (or a first conductivelayer) 406 and an insulator (or a first insulating layer) 408. The firstconductive layer 406 is formed along the first sidewall 404 a of thefirst opening 404 and the first insulating layer 408 is formed along aninner sidewall 406 b of the first conductive layer 406. Accordingly, thefirst conductive layer 406 and the first insulating layer 408 areclosed-shape and concentrically arranged in the first opening 404. Abottom 406 c of the first conductive layer 406 and a bottom 408 c of thefirst insulating layer 408 are positioned on the first bottom 404 b ofthe first opening 404. Sidewall deposition of the first conductive layerand the first insulating layer can be implemented by a selectivedeposition, an atomic layer deposition, or a conformal depositionfollowed by spacer open etches.

In FIG. 3C, the sidewall formation of a conductor and insulator pair(e.g., the first conductive layer and the first insulating layer) isfollowed by a second vertical (directional) etch. Note that theconductor and insulator pair masks (or protects) a portion of the bottomof the first opening 404 so that additional bulk material (e.g.,underlying material with respect to the first opening in the dielectricstack 402) that is etched is narrower than the initial first openingthat was etched, forming a step-shaped etch progression of theunderlying material. As shown in FIG. 3C, the second etch can etch thedielectric stack 402 along an inner sidewall 408 b of the firstinsulating layer 408 so as to form a second opening 410. The secondopening 410 extends into the dielectric stack 402 and has a secondsidewall 410 a and a second bottom 410 b. The second sidewall 410 a isformed along the inner sidewall 408 b of the first insulating layer 408and further extends into the dielectric stack 402. The second bottom 410b of the second opening 410 is positioned below the bottoms 406 c and408 c of the first conductive layer 406 and first insulating layer 408.

These process steps are repeated until all concentric layers arebuilt-up (FIGS. 3D-3H). For example, in FIG. 3D a second conductivelayer 412 is formed along the second sidewall 410 a of the secondopening 410 and a second insulating layer 414 is formed along an innersidewall 412 b of the second conductive layer 412. A bottom 412 c of thesecond conductive layer 412 and a bottom of 414 c the second insulatinglayer 414 are positioned on the second bottom 410 b of the secondopening 410 so that the bottom of the second conductive layer ispositioned below the bottom of the first conductive layer to form astaggered configuration.

In FIGS. 3E-3H, alternately etching the dielectric stack and depositinga conductive layer and an insulating layer sequentially can beperformed. Each deposition and etch operation can be cycled throughsequentially without needed additional lithography exposures.Accordingly, a plurality of conductive layers (e.g., 406, 412, 416, and420) and a plurality of insulating layers (e.g., 408, 414, and 418) areformed in the dielectric stack 402 to meet a predefined number ofconductive layers and a predefined depth. The conductive layers and theinsulating layers are positioned alternately with a closed-shape andconcentrically arranged in the dielectric stack 402. The firstconductive layer 406 is an outermost layer of the conductive layers. Theconductive layers have bottom ends. The bottom ends are staggered andcan be coupled to one or more of the local interconnects (e.g., 324-330in FIG. 2) or one or more of the gate electrodes based on circuitdesigns.

In the example illustrated in FIG. 3A-3H, four conductive structures(also referred to as conductive layers) are formed and three insulatorstructures (also referred to as insulating layers) are formed. Note inFIG. 3H that a coaxial contact structure is formed with a taperedline-end or the coaxial contact structure ends at a tapered bottom-end.This staggered or step-shaped end enables electrical contact todifferent levels (e.g., local interconnects) or lines. This is asimplified example and simplified figures for clarity. In exampleembodiments, a coaxial contact structure herein can be built into apre-existing stack of conductive films such as the local-interconnectlevels (e.g., the local interconnects 324-330) shown in FIG. 2.

In some embodiments, the conductive layers can include tungsten, cobalt,copper, ruthenium, aluminum, or other suitable conductive materials. Theinsulating layers can include SiO, SiN, SiCN, SiC, or other suitabledielectric materials. Any suitable deposition method can be applied toform the conductive layers and the insulating layers, such as chemicalvapor deposition (CVD), physical vapor deposition (PVD), diffusion, andatomic layer deposition (ALD).

FIGS. 4A-4I are cross-sections of substrate segments illustratingformation of line-end extensions on a top level (top end) of the coaxialcontact structure herein. Continuing from FIG. 3H, in FIG. 4A, adielectric capping layer 422 is deposited on the conductive layers(e.g., 406, 412, 416, and 420), the insulating layers (e.g., 408, 414,and 418), and the dielectric stack 402. The dielectric capping layer(also referred to as capping layer) 422 can provide additional etchselectivity such that the bulk dielectric (e.g., the dielectric stack402 that can be made of nitride) can be etched selectively to both thecoaxial insulator (also referred to as insulating layer that can be madeof oxide) and conductor (also referred to conductive layer) withoutaffecting the dielectric capping layer 422. In some embodiments, thecapping layer can be made of one of carbide, SiN, SiC, SiCN or othersuitable dielectric materials. In FIG. 4B, a lithographically definedfirst vertical etch is then executed into the dielectric stack 402surrounding the coaxial contact structure that is formed in FIG. 3H. Thefirst vertical etch can be an anisotropic etch and can be selective tothe conductor (or conductive layer) and coaxial insulators (orinsulating layers) so as to only etch the surrounding dielectric of thecoaxial contact structure or bulk material in the dielectric stack. Asshown in FIG. 4B, the first vertical etch is performed into thedielectric stack to form a vertical trench opening 424 around an outersidewall 406 a of the first conductive layer 406. The vertical trenchopening 424 extends into the dielectric stack 402 with a first depth andexposes a first portion 406 d of the first conductive layer 406.

The initial vertical etch (or first vertical etch) can then be followedby a first isotropic etch (or a first lateral etch) into an outer pairof conductor and insulator (e.g., the first conductive layer 406 and thefirst insulating layer 408), shown in FIG. 4C. In FIG. 4C, the firstlateral etch removes the uncovered first portion 406 d of the firstconductive layer 406 and a first portion of the first insulating layer408 that is adjacent to the uncovered first portion 406 d of the firstconductive layer. The first lateral etch further exposes a first portion412 d of the second conductive layer 412.

In FIG. 4D, a second vertical etch is performed into the dielectricstack 402 to extend the vertical trench opening 424 into the dielectricstack 402 with a second depth and expose (or uncover) a second portion406 e of the first conductive layer 406. The second depth is greaterthan the first depth.

In FIG. 4E, a second lateral etch can be performed. The second lateraletch can remove the exposed (or uncovered) second portion 406 e of thefirst conductive layer 406 and a second portion of the first insulatinglayer 408 that is adjacent to the exposed second portion 406 e of thefirst conductive layer, so as to expose a second portion 412 e of thesecond conductive layer 412. The second lateral etch can further removethe exposed first portion 412 d of the second conductive layer 412 and afirst portion of the second insulating layer that is adjacent to theexposed first portion 412 d of the second conductive layer 412, so as toexpose a first portion 416 d of a third conductive layer 416 of theconductive layers. As mentioned above in FIG. 2, the third conductivelayer 416 is formed along an inner sidewall of the second insulatinglayer 414.

In FIGS. 4F-4H, the process sequence of vertical etch into surroundingmaterial of the coaxial contact structure followed byconductor-insulator pair lateral etch is repeated until all conductivelayers are exposed (uncovered) and can be connected to wires (e.g.,metal layers 316-322 in FIG. 2) that are formed by conventionaldamascene or etch processes. The final step can be to remove thedielectric capping layer 422 as shown in FIG. 4I. Note that a result isthat each coaxial conductor (or conductive layer) has a different heightto enable wire connections at different metal levels, thereby providingself-alignment of contacts also. After the removal of the dielectriccapping layer 422, a coaxial contact 400 can be formed in FIG. 4I. Thecoaxial contact 400 can have a similar configuration to the coaxialcontact 300 in FIG. 2.

FIGS. 5A and 5B illustrate how the coaxial contact structure herein canbe used to build very compact 3D integrated logic layouts. FIG. 5A is aschematic circuit diagram of an And-Or-Invert 22 (AOI22) cell 500. TheAOI cell 500 herein is a moderately complex standard cell withtransistors that are grouped in parallel pairs on a p-fet side of thecell and serial pairs on a n-fet side of the cell. For example, thep-fet side can includes four p-type transistors P1-P4, where P1 and P2are connected in parallel, and P3 and P4 are connected in parallel. Then-fet side can includes four n-type transistors N1-N4, where N1 and N2are serially connected and N3 and N4 are serially connected. The AOIcell (or AOI22 cell) 500 is electrically coupled to four inputs A-D andan output Y. Each of the four inputs A-D is coupled to a respectiven-type gate and p-type gate of the AOI cell 500. For example, the inputA is coupled to a n-type gate of n-type transistor N1 and a p-type gateof p-type transistor P1. In addition. The AOI cell 500 is connected to asupply voltage VDD that are coupled to source regions of the p-typetransistors P1 and P2. The AOI cell 500 is further connected to a groundvoltage GND that is coupled to source regions of the n-type transistorsN2 and N4.

FIG. 5B is a top down layout view 600 of an AOI22 cell that isimplemented based on a CFET stack and coaxial contacts, in accordancewith some embodiments of the present disclosure. The layout view 600 caninclude a plurality of coaxial contacts 602-610, an active region 611that has doped through an ion implantation process. In some embodiments,the coaxial contacts 608 and 610 can be source-side coax-contacts thatare coupled to source regions of the CFET stack, the coaxial contacts604 and 606 can be drain-side coax-contacts that are coupled to drainregions of the CFET stack, and the coaxial contacts 602 and 607 can begate coax-contacts that are coupled to gate electrodes of the CFETstack. The layout view 600 can have a poly gate 612 which is an overlapof several poly gates shown in FIGS. 6A-6D, a plurality of metal one(M1) layers 614-620 that are coupled to one or more inputs (e.g., inputsA-C) and an output (e.g., output Y). The layout view 600 can furtherhave a plurality of metal zero (M0) layers 622-628, one or moreinterconnects (or vertical interconnects, or vertical outputinterconnects) 630-632, source-side/drain-side local interconnects (alsoreferred to as source/drain local interconnects) 634-636 for n-typetransistors of the CFET stack, source-side/drain-side localinterconnects 638-640 for p-type transistors of the CFET stack, apower-rail connection 642 coupled to a supply voltage VDD and apower-rail connection 644 coupled to a ground voltage GND.

FIG. 5B shows an AOI22 (i.e. and-or invert) cell identifying someattributes that can be further described in FIGS. 6A-6D. The logic cellshown in FIG. 5B is 4 metal tracks tall and 3 poly tracks wide. Spaceleft by a diffusion break, which can be left and right margins of thecell outside the active area/region, is used to connect to buried orconventional power-rails (not shown). Using a metal to poly pitch ratioof 2:1 leaves 5 tracks for metal to form four inputs (e.g., A-D) and oneoutput (e.g., Y) pin. A manner of connecting coaxial contacts with thesepins to a 3D stack of active devices is illustrated in FIGS. 6A-6D. Alsoillustrated in FIGS. 6A-6D is a manner in which source and drainconnections are formed to render desired or designed logic functions.

FIGS. 6A-6D use four cross-section cut-lines, one for each of the metaltracks, to illustrate how the coaxial contact is used to form verycompact logic cells and to show the highly efficient and ultra-regularunidirectional local wiring layout configurations which the coaxialcontact enables. To be able to put specific connection points intocontext, a top-down layout view 600 of the AOI22 cell, as shown in FIG.5B, is repeated in FIGS. 6A-6D with a location of respective coaxcontacts highlighted. In general, the coaxial contacts provide an areaefficient connection between a stack of generic devices and a stack oflocal wiring which functionalizes each cell with a high degree ofpatterning and process efficiency.

In FIG. 6A, a connection from input pins A and B to a corresponding polygate is shown. The top portion of FIG. 6A is the layout view 600 of theAOI22 cell, and the bottom portion of FIG. 6A is a cross-sectional viewthat is obtained from a line A-A′ perpendicular to a top surface of thelayout view 600. Input pins (labeled A and B) can be M1 level andapplied with corresponding inputs (e.g., A-D). In FIG. 6A, input pin A(i.e., 614) and input pin B (i.e., 616) connect through conventionalvertical interconnects (e.g., vias) 646 and 648 to a corresponding lowerlevel of metal, such as M0 level 622 and 624 respectively. The verticalinterconnects 646 and 648 can also be referred to as inter-levelconnection points. For example, the input pin A 614 is connected to M0level (or M0 layer) 622 through the vertical interconnect 646. The twolevels of M0 (e.g., 622 and 624) then connect to the two concentrictubes of conductor (or conductive layers) in the coaxial contact 602.Accordingly, input pin A connections to an outer conductor (outerconductive layer), while input pin B connects to an inner conductor ofthe coaxial contact 602. Further, the outer conductor is coupled to thepoly gate A and the inner conductor is coupled to the poly gate Brespectively. Therefore, the design in FIG. 6A provides anarea-efficient connection between the input pins and gate levels A andB.

FIG. 6B illustrates power, internal wiring, and output signalconnections to p-type devices. The top portion of FIG. 6B is the layoutview 600 of the AOI22 cell, and the bottom portion of FIG. 6B is across-sectional view that is obtained from a line B-B′ perpendicular tothe top surface of the layout view 600. Power (or supply voltage) VDDenters devices from the power-rail connection 642 appearing on the leftside of the cross section through lower two M0 levels 650 a-650 b. PowerVDD connections are strapped to outer two conductive layers in thecoaxial contact 610 and routed to the source-side local interconnects638 for gates A and B. After running through gates A and B in parallel(as called for on the p side of the schematic), the output is picked upby the drain-side local interconnects 640 for gates A and B. The outputis then picked up by the coaxial contact 604 and then is routed to thebottom two M0 levels 650 e-650 f. The two M0 levels 650 e-650 f arefurther connected to the top two M0 levels 650 c-650 d through one ormore vertical interconnects (or inter-level connection points) 652 a-652c. Moving the signal (e.g., power VDD) from the bottom two M0 levels 650e-650 f to the top two M0 levels 650 c-650 d allows the signal to be fedinto the inner two conductive layers of the coaxial contact 610. Theinner two conductive layers of the coaxial contact 610 are coupled tothe source-side local interconnects 638 for gates C and D to provideinput to gates C and D. The outputs of gates C and D in turn are pickedup by the drain-side local interconnects 640, and further picked up bytwo inner conductive layers of the coaxial contact 604. The outputs arefurther routed by the two inner conductive layers of the coaxial contact604 to two top M0 levels 650 g-650 h, and further are fed to the outputpin Y (e.g., 620). It should be noted that the two top M0 levels 650g-650 h are coupled to the output pin Y through interconnects 630.

FIG. 6C illustrates power, internal wiring, and output signalconnections to n-type devices. The top portion of FIG. 6C is the layoutview 600 of the AOI22 cell, and the bottom portion of FIG. 6C is across-sectional view that is obtained from a line C-C′ perpendicular tothe top surface of the layout view 600. Power enters from GND power-railconnection 644 through second and third M0 levels 654 a-654 b. Thesecond and third M0 levels 654 a-654 b connect the power-rail connection644 to the source-side local interconnects 634 for gates C and B throughthe coaxial contact 608. After running through gates C and B, output ispicked up by the drain-side local interconnects 636 for gates C and B.The output is then fed by coaxial contact 606 that is connected with thedrain-side local interconnects 636 to 2nd and 3rd M0 levels 654 e-654 f.The 2nd and 3rd M0 levels 654 e-654 f are further strapped to the topand bottom M0 levels 654 c and 654 d through vertical interconnects(also referred to as inter-level connection points) 656 a-656 brespectively. The top and bottom M0 levels 654 c and 654 d are thenconnected to the source-side local interconnects 634 for gates A and Dthrough the coaxial contact 608 and the output accordingly becomes aninput to gates A and D. An output of gates A and D is then picked up bythe drain-side local interconnects 636 for gates A and D, and furtherpicked up by the outer and inner most conductive layers of the coaxialcontact 606 that are connected with the drain-side local interconnects636. The coaxial contact 606 routes the output of gates A and D to thetop and bottom M0 levels 654 g and 654 h. The top and bottom M0 levels654 g and 654 h further route the output of gates A and D to the outputpin Y (e.g., 620), where the top and bottom M0 levels 654 g and 654 hare coupled to the output pin Y through the interconnect 632.

FIG. 6D illustrates configuration and functionality similar to FIG. 6A.The top portion of FIG. 6D is the layout view 600 of the AOI22 cell, andthe bottom portion of FIG. 6D is a cross-sectional view that is obtainedfrom a line D-D′ perpendicular to a top surface of the layout view 600.Similar to FIG. 6A, signal connections to gates C and D through thecoaxial contact 607, where an outer conductor of the coaxial contact 607connects the bottom M0 layer 626 to the gate C, and a center conductor(or conductive layer) of the coaxial contact 607 connects the top-mostM0 628 to the bottom-most gate D. As shown in FIG. 6D, input pins(labeled C and D) 617-618 can be M1 level (or M1 layer) and applied withcorresponding inputs (e.g., C and D). The input pin C 618 and input pinD 617 connect through conventional vertical interconnects 660 a and 660b to corresponding lower level of metal M0 628 and 626 respectively. Forexample, the input pin C 618 is connected to M0 628 through the verticalinterconnect 660 a. The two levels of M0 (e.g., 626 and 628) thenconnect to the two concentric tubes of conductor (or conductive layers)in the coaxial contact 607. Accordingly, input pin C 618 connects to anouter conductor (outer conductive layer), while input pin D 617 connectsto an inner conductor of the coaxial contact 607. Further, the outerconductor is coupled to the poly gate D and the inner conductor iscoupled to the poly gate C respectively. Therefore, the design in FIG.6D provides an area-efficient connection between the input pins and gatelevels C and D.

Accordingly technique herein includes methods of fabrication andsemiconductor device structures. One embodiment includes a verticalinterconnect structure. The vertical interconnect structure comprisesmultiple concentric conductive layers separated by insulators (orinsulating layers). The interconnect structure has staggered ends (lineends or structure ends), that is, step-shaped ends. Such staggeringfacilitates selective connectivity to subsequent conductive layers(e.g., source-side or drain-side local interconnect) in a stack.

Another embodiment includes a microfabrication process to form bottomline-end extensions. The process includes a first etch that is adirectional (anisotropic) etch to define an opening/hole in a firstdielectric material. The first etch forms the opening sufficient for aradius of a coaxial contact structure, but at a partial depth of a finalcoaxial contact structure. The depth can be equivalent to a depth of anouter conductor (or conductive layer) of the coaxial contact structureto be formed. Depositing a first conductor on sidewalls of the opening,and depositing a first insulator (or insulating layer) on uncoveredsidewalls of the first conductor. Executing a second etch (directional)that removes portions of the first dielectric material not covered bythe first conductor and the first insulator. The second etch etching apredetermined distance into the first dielectric. Depositing a secondconductor on sidewalls of the first insulator and uncovered sidewallportions of the opening. Depositing a second insulator on uncoveredsidewalls of the second conductor. Filling space remaining in thedefined opening with a third conductor. Note that additional conductorand insulator pairs can be added prior to filling remaining space withthe third conductor. The defined opening is further etched prior to eachadditional conductor and insulator pair, and the defined opening isfurther etched prior to a final fill (filling with third conductor).

Another embodiment includes a process for forming a top (vertical top)of a coaxial contact structure herein. The process begins with a coaxialcontact structure having concentric formations of conductor andinsulator pairs and having a planar top surface. The bottom of thecoaxial contact structure can be step-shaped with a central conductorextending deeper compared to an outer conductor. The coaxial contactstructure is surrounded by a first dielectric material. A first etch (ora directional etch, a vertical etch) is executed into the firstdielectric material surrounding the coaxial contact structure. The firstetch can etch to a predetermined depth, such as a vertical depth of onelateral wiring and dielectric layer. Next, as second etch is executedthat is a lateral etch into an outermost coaxial conductor and insulatorpair. A third etch is executed that is a vertical etch into the firstdielectric surrounding the coaxial contact structure to a depth of anadditional lateral wiring and dielectric layer. A fourth etch is executethat is a lateral etch into each uncovered conductor and insulator pair,resulting in a step-shaped geometry of a top end of the coaxial contactstructure. This sequence of vertical etch into surrounding dielectricfollowed by lateral/horizontal etching of uncovered conductor anddielectric pairs is executed until uncovering a central conductor of thecoaxial contact structure. In addition to the central conductor, thecoaxial contact structure can include one or more conductor andinsulator cylindrical pairs.

Another embodiment includes a device design or configuration. Such adesign, for example, can be used as a standard cell architecture (e.g.,a AOI22 cell) or part of a standard cell architecture. Such a device caninclude a power-rail connection (e.g., 642 and 644 in FIG. 5B). Thepower-rail connection can be positioned in a space left by a diffusionbreak on one vertical cell boundary (referred to herein as a“source-side” of a cell). The power-rail connection is split between VDD(high voltage, also referred to as 1) over p-devices (or p-typetransistors), and GND (low voltage, also referred to as 0) over then-devices (or n-type transistors). The power-rail connection genericallyextends over an entire height of the local wiring (M0) stack, allowingfunctionalization solely by connecting the appropriate M0 levels.

A vertical interconnect (or vertical output interconnect) (e.g., 630,632 in FIG. 5B) is positioned on an opposite side of the cell (referredto herein as the “drain-side” of the cell) connecting both p-devices andn-devices to an output pin (e.g., 620 in FIG. 6B). The verticalinterconnect is formed either as two separate connections of p and nregions of the cell or one continuous via-bar connecting both outputssimultaneously. The vertical output interconnect (e.g., 630 or 632 inFIG. 5B) generically extends over an entire height of the local wiring(M0) stack, allowing functionalization by connecting corresponding M0levels.

A stack of local wiring (M0) levels (e.g., 654 a-654 d in FIG. 6C) isformed with one wiring level per device level in a 3D logic stack (i.e.stacking four transistors requires four levels of M0). Such M0 levelsfacilitate functionalization of the cell layout by forming fourconnections over both the p-device and n-device local interconnects(e.g., 638 and 640 in FIG. 6B, 634 and 636 in FIG. 6C). The connectionsmade by M0 levels can include a power (e.g., VDD or GND) to asource-side coax-contact (e.g., 608 and 610), a drain-side coax-contact(e.g., 604 and 606) to an inter-level connection point (e.g., 652 a-652c in FIG. 6B), an inter-level connection point (e.g., 656 b in FIG. 6C)to a source-side coax-contact (e.g., 608), and a drain-side coax-contact(e.g., 606) to a vertical interconnect (e.g., 632) connected to outputpin (e.g., 620). These M0 levels further connect the input pins (e.g.,614-618) of the cell to the appropriate transistor gates (e.g., polygates A-D) through gate coax-contacts (e.g., 602, 607) on wiring tracksoutside the active region (e.g., 611) of the cell/device.

In the present disclosure, a pair of gate coax-contacts (e.g., 602 and607) is positioned, one over each outside wiring track, to connectstacked gates to the input pins. And two or more pairs of source/draincoax-contacts are formed, where one pair (e.g., 610 and 604) ispositioned over the p-device source and drain, the other pair (e.g., 608and 606) is positioned over the n-device source and drain.

Accordingly, techniques herein provide a compact and efficient methodand structure for providing vertical connections within varioussemiconductor devices including 3D logic devices as well as memorydevices such as static random access memory (SRAM) devices.

In the preceding description, specific details have been set forth, suchas a particular geometry of a processing system and descriptions ofvarious components and processes used therein. It should be understood,however, that techniques herein may be practiced in other embodimentsthat depart from these specific details, and that such details are forpurposes of explanation and not limitation. Embodiments disclosed hereinhave been described with reference to the accompanying drawings.Similarly, for purposes of explanation, specific numbers, materials, andconfigurations have been set forth in order to provide a thoroughunderstanding. Nevertheless, embodiments may be practiced without suchspecific details. Components having substantially the same functionalconstructions are denoted by like reference characters, and thus anyredundant descriptions may be omitted.

Various techniques have been described as multiple discrete operationsto assist in understanding the various embodiments. The order ofdescription should not be construed as to imply that these operationsare necessarily order dependent. Indeed, these operations need not beperformed in the order of presentation. Operations described may beperformed in a different order than the described embodiment. Variousadditional operations may be performed and/or described operations maybe omitted in additional embodiments.

“Substrate” or “target substrate” as used herein generically refers toan object being processed in accordance with the invention. Thesubstrate may include any material portion or structure of a device,particularly a semiconductor or other electronics device, and may, forexample, be a base substrate structure, such as a semiconductor wafer,reticle, or a layer on or overlying a base substrate structure such as athin film. Thus, substrate is not limited to any particular basestructure, underlying layer or overlying layer, patterned orun-patterned, but rather, is contemplated to include any such layer orbase structure, and any combination of layers and/or base structures.The description may reference particular types of substrates, but thisis for illustrative purposes only.

Those skilled in the art will also understand that there can be manyvariations made to the operations of the techniques explained abovewhile still achieving the same objectives of the invention. Suchvariations are intended to be covered by the scope of this disclosure.As such, the foregoing descriptions of embodiments of the invention arenot intended to be limiting. Rather, any limitations to embodiments ofthe invention are presented in the following claims.

What is claimed is:
 1. A semiconductor device formed over a substrate,comprising: conductive layers extending from local interconnects andcoupled to metal layers that are stacked over the local interconnects,the local interconnects being stacked over the substrate and extendinglaterally along a top surface of the substrate, the metal layersextending laterally along the top surface of the substrate, theconductive layers being close-shaped, concentrically arranged, andextending in a pillar shape, each of the local interconnects beingcoupled to a corresponding conductive layer from the conductive layers,and each of the conductive layers being coupled to a corresponding metallayer from the metal layers; and insulating layers that areclose-shaped, concentrically arranged, and positioned alternately withrespect to the conductive layers so that the conductive layers arespaced apart from one another by the insulating layers.
 2. Thesemiconductor device of claim 1, wherein the conductive layers havebottom ends, the bottom ends being staggered and coupled to one or moreof the local interconnects so that each of the local interconnects iscoupled to a respective conductive layer from the conductive layers. 3.The semiconductor device of claim 2, wherein the insulating layers havebottom ends, the bottom ends being staggered so that a bottom end ofeach of the insulating layers is level with a bottom end of acorresponding conductive layer from the conductive layers.
 4. Thesemiconductor device of claim 1, wherein the conductive layers have topends, the top ends being staggered and coupled to one or more of themetal layers so that each of the conductive layers is coupled to arespective metal layer from the metal layers.
 5. The semiconductordevice of claim 4, wherein the insulating layers have top ends, the topends being staggered so that a top end of each of the insulating layersis level with a top end of a corresponding conductive layer from theconductive layers.
 6. The semiconductor device of claim 1, wherein theconductive layers have at least one of a tube configuration, or acylinder configuration.
 7. The semiconductor device of claim 6, whereinthe tube configuration or the cylinder configuration has a taperedprofile.
 8. The semiconductor device of claim 1, further comprising:transistor pairs that are stacked over the substrate, each of thetransistor pairs including a n-type transistor and a p-type transistorthat are stacked over one another, wherein: the n-type transistor has asource region and a drain region that are positioned at two ends of an-type channel region of the n-type transistor, each of the sourceregion and drain region of the n-type transistor being coupled to arespective local interconnect from the local interconnects, the n-typechannel region being surrounded by a n-type gate structure, and thep-type transistor has a source region and a drain region that arepositioned at two ends of a p-type channel region of the p-typetransistor, each of the source region and drain region of the p-typetransistor being coupled to a respective local interconnect from thelocal interconnects, the p-type channel region being surrounded by ap-type gate structure.
 9. The semiconductor device of claim 8, furthercomprising: gate electrodes that are stacked over the substrate, thegate electrodes being electrically coupled to gate structures of thetransistor pairs, wherein at least one of the conductive layers extendsfrom one of the gate electrodes, and is coupled to the one of the gateelectrodes.
 10. A method for forming a semiconductor device, comprising:forming a first opening in a dielectric stack over a substrate, thefirst opening has a cylinder shape with a first sidewall and a firstbottom; depositing a first conductive layer along the first sidewall ofthe first opening and a first insulating layer along an inner sidewallof the first conductive layer so that the first conductive layer and thefirst insulating layer having closed-shape and concentrically arranged,a bottom of the first conductive layer and a bottom of the firstinsulating layer being positioned on the first bottom of the firstopening; etching the dielectric stack along an inner sidewall of thefirst insulating layer so as to form a second opening, the secondopening extending into the dielectric stack and having a second sidewalland a second bottom, the second sidewall being formed along the innersidewall of the first insulating layer and further extending into thedielectric stack, the second bottom of the second opening beingpositioned below the bottoms of the first conductive layer and firstinsulating layer; and depositing a second conductive layer along thesecond sidewall of the second opening and a second insulating layeralong an inner sidewall of the second conductive layer, a bottom of thesecond conductive layer and a bottom of the second insulating layerbeing positioned on the second bottom of the second opening so that thebottom of the second conductive layer is positioned below the bottom ofthe first conductive layer to form a staggered configuration.
 11. Themethod of claim 10, further comprising: alternately etching thedielectric stack and depositing a conductive layer and an insulatinglayer sequentially so that a plurality of conductive layers and aplurality of insulating layers are formed in the dielectric stack tomeet a predefined number of conductive layers and a predefined depth,the conductive layers and the insulating layers having a concentricallyclosed-shape and being positioned alternately, the first conductivelayer being an outermost layer of the conductive layers, the conductivelayers having bottom ends, the bottom ends being staggered and extendingfrom one or more of local interconnects so that each of the localinterconnects is coupled to a respective conductive layer, the localinterconnects being stacked over the substrate and extending laterallyalong a top surface of the substrate.
 12. The method of claim 11,further comprising: depositing a dielectric capping layer over theinsulating layers, the conductive layers and the dielectric stack,wherein the insulating layers, the conductive layers and the dielectricstack are coplanar; performing a first vertical etch into the dielectricstack to form a vertical trench opening around an outer sidewall of thefirst conductive layer; the vertical trench opening extending into thedielectric stack with a first depth and uncover a first portion of thefirst conductive layer; performing a first lateral etch to remove theuncovered first portion of the first conductive layer and a firstportion of the first insulating layer that is adjacent to the uncoveredfirst portion of the first conductive layer, wherein the first lateraletch further uncovers a first portion of the second conductive layer;performing a second vertical etch into the dielectric stack to extendthe vertical trench opening into the dielectric stack with a seconddepth and uncover a second portion of the first conductive layer; andperforming a second lateral etch, wherein the second lateral etchremoves (i) the uncovered second portion of the first conductive layerand a second portion of the first insulating layer that is adjacent tothe uncovered second portion of the first conductive layer, so as touncover a second portion of the second conductive layer, and (ii) theuncovered first portion of the second conductive layer and a firstportion of the second insulating layer that is adjacent to the uncoveredfirst portion of the second conductive layer, so as to uncover a firstportion of a third conductive layer of the conductive layers, the thirdconductive layer being formed along an inner sidewall of the secondinsulating layer.
 13. The method of claim 12, further comprising:alternately performing a vertical etch and a lateral etch so that eachof the conductive layers is uncovered in the vertical trench opening,and top ends of the conductive layers are staggered and coupled to oneor more of metal layers so that each of the conductive layer is coupledto a respective metal layer from the metal layers, wherein the metallayers are stacked over the local interconnects.
 14. The method of claim13, furthering comprising: forming transistor pairs that are stackedover the substrate, each of the transistor pairs including a n-typetransistor and a p-type transistor that are stacked over one another,wherein: the n-type transistor has a source region and a drain regionthat are positioned at two ends of a n-type channel region of the n-typetransistor, each of the source region and drain region of the n-typetransistor being coupled to a respective local interconnect, the n-typechannel region being surrounded by a n-type gate structure, and thep-type transistor has a source region and a drain region that arepositioned at two ends of a p-type channel region of the p-typetransistor, each of the source region and drain region of the p-typetransistor being coupled to a respective local interconnect, the p-typechannel region being surrounded by a p-type gate structure.
 15. Themethod of claim 14, further comprising: forming gate electrodes that arestacked over the substrate, the gate electrodes being electricallycoupled to gate structures of the transistor pairs, wherein at least oneof the conductive layers extends from one of the gate electrodes, and iscoupled to the one of the gate electrodes.
 16. A semiconductor device,comprising: transistor pairs that are stacked over a substrate, each ofthe transistor pairs including a n-type transistor and a p-typetransistor that are stacked over one another, local interconnects beingstacked over the substrate and extending along a top surface of thesubstrate, the local interconnects being electrically coupled to sourceregions and drain regions of the transistor pairs; metal layers stackedover the local interconnects; conductive layers extending from the localinterconnects and coupled to the metal layers, the conductive layersbeing close-shaped, concentrically arranged, and extending in a pillarshape, each of the local interconnects being coupled to a correspondingconductive layer from the conductive layers, and each of the conductivelayers being coupled to a corresponding metal layer from the metallayers; and insulating layers being close-shaped, concentricallyarranged, and positioned alternately with respect to the conductivelayers so that the conductive layers are spaced apart from one anotherby the insulating layers.
 17. The semiconductor device of claim 16,wherein the conductive layers have bottom ends, the bottom ends beingstaggered and coupled to one or more of the local interconnects so thateach of the local interconnects is coupled to a respective conductivelayer from the conductive layers.
 18. The semiconductor device of claim16, wherein the conductive layers have top ends, the top ends beingstaggered and coupled to one or more of the metal layers so that each ofthe conductive layer is coupled to a respective metal layer from themetal layers.
 19. The semiconductor device of claim 16, wherein theconductive layers have at least one of a tube configuration, or acylinder configuration.
 20. The semiconductor device of claim 16,further comprising: gate electrodes that are stacked over the substrate,the gate electrodes being electrically coupled to gate structures of thetransistor pairs, wherein at least one of the conductive layers extendsfrom one of the gate electrodes, and is coupled to the one of the gateelectrodes.